GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

2.1.8 The Broader Legacy of GP-BWhen the GP-B experiment was first conceived in late 1959- 1960, the United States had just created NASA,launched its first satellite, and entered the space race. Landing men on the Moon was still nine years away. Atthe time, this experiment seemed rather simple, but it has taken over four decades of scientific and technologicaladvancement to create a space-borne laboratory and measurement instrument sophisticated and preciseenough to carry out these minuscule measurements of relativistic effects around the Earth.At least a dozen new technologies had to be invented and perfected in order to carry out the Gravity Probe Bexperiment. For example, the spherical gyroscopes have a stability that is more than a million times better thanthe best inertial navigation gyroscopes. The ping-pong-ball-sized gyroscope rotors in these gyroscopes had to beso perfectly spherical and homogeneous that it took more than10 years and a whole new set of manufacturingtechniques to produce them. They’re now listed in the Guinness Database of Records as the world’s roundestman-made objects.The magnetometers, called SQUIDs (Super-Conducting Quantum Interference Devices), monitor the spin axisdirection of the gyroscopes and can detect—digitally—a change in spin axis alignment to an angle ofapproximately 1/40,000,000 th of a degree. These advances were only possible through GP-B’s uniquecombination of cryogenics, drag-free satellite technology, as well as totally new manufacturing and measuringtechnologies.Similarly, it took two years to make the flawless roof prisms in the GP-B science telescope that tracks the guidestar. Some scientists have mused about how Einstein, himself once a patent clerk, would have enjoyed reviewingthese extraordinary technologies. See Chapter 3, GP-B’s Unique Technological Challenges and Solutions fordescriptions of 12 key GP-B unique technological innovations.Over its 40+ year life span, spin-offs from the Gravity Probe B program have yielded many technological,commercial, and social benefits. For example, optical-bonding and fused-quartz technologies pioneered for GP-B have subsequently been applied to commercial products, and photo-diode detector technology developed foruse in the GP-B telescope has had ramifications for digital camera improvements. Another example is GP-B'sporous plug for controlling helium in space. This cryogenic technology was essential to several other vital NASAmissions, including IRAS (Infrared Astronomical Satellite) and COBE (COsmic Background Explorer).One interesting GP-B spin-off story is the evolution of precision guidance control technology from testingEinstein to plowing fields. Under the supervision of GP-B Co-PI, Brad Parkinson, centimeter-accurate GlobalPositioning Satellite (GPS) technology, originally developed for attitude control of the GP-B spacecraft, was repurposedfor other automated guidance control applications in the early 1990’s by Clark Cohen and a group ofhis fellow GP-B/GPS graduate students at Stanford. After receiving his Ph.D., Cohen founded a company, nowNovariant Corporation, to develop precision GPS guidance control applications, such as an automatic aircraftlanding system and automated precision farming.Figure 2-15. Stanford GP-B/GPS graduate students and a faculty member pose next to a GPS-controlled tractor;Clark Cohen (left) and Brad Parkinson (right) receive awards from the Space Technology Hall of Fame.42 March 2007 Chapter 2 — Overview of the GP-B Experiment & Mission